A variety of systems are now known for the installation of underground pipes, particularly for the replacement of an existing deteriorated pipe. Directional boring apparatus for making holes through soil are well known and are used to replace existing pipe. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled through the soil by means of a powerful hydraulic device such as a hydraulic cylinder. See Malzahn U.S. Pat. Nos. 4,945,999 and 5,070,948, and Cherrington U.S. Pat. No. 4,697,775 (RE 33,793). The drill string may be pushed and rotated at the same time as described in Dunn U.S. Pat. No. 4,953,633 and Deken et al. U.S. Pat. No. 5,242,026. A spade, bit or head configured for boring is disposed at the end of the drill string and which may include an ejection nozzle for water to assist in boring.
In one variation of the traditional boring system, a series of drill string rods is used in combination with a percussion tool mounted at the end of the series of rods. The rods can supply a steady pushing force to the impact tool and the interior of the rods can be used to supply the pneumatic borer with compressed air. See McDonald et al., U.S. Pat. No. 4,694,913. This system has, however, found limited application commercially, perhaps because the drill string tends to buckle when used for pushing if the bore hole is substantially wider than the diameter of the drill string.
In one widely practiced method, a pneumatic impact boring tool such as a "Hammerhead Mole" (a registered trademark of Earth Tool Co.) boring tool is sent through the existing pipeline such that the head of the tool, which may be provided with blades that apply intense local pressure to the existing pipe, fractures or splits the existing pipe. See Streatfield et. al., U.S. Pat. Nos. 4,720,211, 4,738,565 and 4,505,302. A replacement pipe, typically made of plastic such as HDPE, can be drawn along behind the boring tool. Pneumatic impact boring tools are well known and are, for example, described in Wentworth et al. U.S. Pat. Nos. 5,025,868 or 5,337,837. The Streatfield et al. process has proven effective commercially because it bursts the old pipe into a multitude of fragments and replaces it with a new pipe at the same time. However, the system relies on a pneumatic impact tool, which in turn requires an air compressor. Exhaust from the impact tool is vented into the interior of the replacement pipe, which is unacceptable for certain types of pipe installations, such as gas and water lines. The Streatfield et al. method is also less effective on ductile or non-frangible pipes such as copper, lead and certain types of plastic, such as HDPE.
Directional borers are less effective for pipe bursting, especially for hard to burst pipes like cast iron, because the steady pushing force of the drill string lacks the impact power of a pneumatic impact boring tool. Thus, in some instances, a directional borer or winch is used to pull a pneumatic impact tool through a existing pipeline in order to burst the existing pipe and pull in the replacement pipe. These alternatives are effective but require considerable equipment and manual labor.
Expanders are tapered, ring-shaped shells that fit over the tapered nose portion of a pneumatic earth boring tool in order to widen the hole made by the tool as it passes through the ground. In this manner, a 4-inch diameter tool may be used to make a 6- or 8-inch diameter hole. The tool is often sent through to make an initial bore, and then sent through a second time with the expander in order to widen the existing hole and/or crack an existing pipe. A plastic pipe may be attached to the back of the expander with the above described reversible tool inside the pipe so that the pipe is installed as the tool bores through the soil, with or without additional widening of the bore. The tool body is disposed inside the replacement pipe, and in this arrangement friction between the expander and the soil serves to keep the tool and expander from moving backward during the rearward stroke of the striker.
Problems are encountered as the tool advances further into the ground and the weight of the pipe being drawn behind the tool grows progressively greater. The ground piercing tool relies on friction with the surrounding soil to prevent it from moving backward during the rearward stroke of the striker the same distance the tool moved forward when the striker made its forward impact. The elasticity of the pipe drawn behind the tool can counteract this frictional force, slowing and eventually stopping the tool.
To remedy this difficulty, it is known to attach a cable to the front end of the impact ground piercing tool and use a winch to apply a continuous pulling force to the tool in the forward direction. The cable is threaded through the existing pipeline or a pilot hole and serves to keep the tool moving and prevent it from deviating from its proper course. While it is possible to push on the existing pipeline from behind instead of pulling on the ground piercing tool using a cable, the pushing operation is less effective because it increases the chance that the ground piercing tool will deviate from the desired path.
A less widely known tool makes use of a splitting wedge to separate the old pipe while simultaneously expanding the ground pulling in and replacement pipe. A wire rope as large as the old pipe will accommodate is passed through the inside of the pipe, and a splitter/expander/pipe puller mechanism is attached to the end of the rope. The free end is attached to a backhoe or pickup truck. Such a method of pulling is usually very disturbing to the traffic flow in the area used. The splitter is pulled through the ground, performing the splitting, expanding and pulling functions as described. The old pipe is slit rather than shattered into fragments, and remains in the ground after the wedge has passed. This device is known as `The Wedge` Tool and is offered by Footage Tools of Canada.
There are several weaknesses or disadvantages in using Footage Tool device. Because there are large pieces of equipment moving great distances in a direction perpendicular to street traffic, there will be safety concerns. Clearance space in the enlarged bore is needed to accommodate both the new pipe and old split pipe. Failure to create this clearance can result in breaking the new pipe as the process gets further into the bore. Friction between the old pipe, the ground and the new pipe will hold the new pipe back and continually increase the tensile load on the new pipe. The old pipe split sections tend to `clutter` the bore as they are now irregularly shaped. The need to create a large bore means additional pulling force must be applied to the wire rope. Unfortunately, in most cases the existing pipe is small in diameter. Therefore, the wire rope must be small as well. This combination of high pulling forces required to create a large bore and using a small wire cable often results in a broken cable.
The present inventors have discovered that this technique, despite its apparent simplicity, is slow and fraught with problems. First, the need for heavy equipment is not avoided. The backhoe or winch truck must be positioned above a fairly large exit pit. The exit pit for a gas line is typically near the gas main and thus near the street, so the prior methods may require tearing up a large section of roadway and/or blocking traffic with equipment.
This method also is prone to jamming and breakage of the cable. The present inventors have discovered that ductile pipes such as plastic, when slit, tend to bunch up against the new pipe as it is drawn into place, eventually causing the wedge to become stuck or the cable to break. The present invention addresses these drawbacks.